The present invention relates generally to printer output devices, and more particularly to a print media stacker apparatus which prevents a user from having access to an output sheet until the printing operation is complete.
In many applications of printing devices, it is desirable that printed documents being output from the printing device not be accessible to a user until the printing operation is complete. If an over-anxious user pulls on a document while the printing operation is on-going, it is likely that the print media or substrate upon which the printing is being disposed will shift unpredictably relative to the printing device, and the quality of the printed document will be compromised. Furthermore, if the document is being printed and subsequently cut from a continuous roll of stock, pulling of the document from the printer before the cutting process is complete is likely to cause uneven cuts and possibly jamming of the document delivery device.
It is known in the art to provide printing devices with document delivery mechanisms which prevent a user from obtaining access to the document being printed and delivered from the printing device until printing and cutting operations are complete. For example, U.S. Pat. No. 5,215,393 (Wincent) (“the '393 patent”) discloses a device for feeding documents, such as receipts or tickets, to a user from a printing apparatus. The invention of Wincent comprises means for preventing a user from having access to the printed receipt until the printing operation is complete and the receipt has been severed from a continuous roll of receipt paper stock. The invention of Wincent relies upon the printed document bowing upwardly in a predictable manner as illustrated in FIG. 1 of the '393 patent, and thus requires that the printed document be printed on a substrate having sufficient stiffness and being sufficiently short to allow the document to bow upward in an arc as shown.
A deficiency of the prior art is the inability of the document output devices to accommodate a combination of relatively light paper stock along with elongated document dimensions. For example, use of a less stiff paper stock or printing of documents substantially elongated relative to the proportions disclosed by Wincent would result in the upwardly bulged portion P2 in FIG. 1 collapsing in a generally unpredictable configuration, resulting in a significant probability of the document becoming jammed or the printed document being wrinkled or otherwise damaged.
There is a need, therefore, for an apparatus which would provide the benefits of preventing a user from obtaining access to a printed document until the printing and cutting operations are fully completed, but which would also accommodate a wide range of media or substrate stock weights and lengths.